This invention pertains generally to document imaging systems, and more particularly to electro-optical document imaging systems incorporating transparent document support platens.
Document imaging systems, that is, electro-optical systems that sense and process the visual appearance of documents and/or other objects presented to them, have progressed far beyond the original black and white analog copier. This category of devices now also includes digital facsimile devices, black and white and color scanners that capture documents to electronic form, digital copiers, color copiers, and devices that can function as two or more of these devicesxe2x80x94some also functioning as printers.
Most document imaging systems generally detect the content of an image by scanning, i.e., providing for relative movement between the document and one or more detectors. In some imaging systems, including historically, most facsimile machines, the document is fed past the detectors a scan line at a time, or at a known rate. In other imaging systems, the document remains stationary on a flat bed, or transparent support platen, while the detector is manipulated below the platen.
Flatbed systems have several advantages. They can accept a wide variety of shapes, sizes, textures, and thicknesses of documents, including books and fragile or valuable documents that could be damaged by a feeder. Also, document feeders rely on friction drive, but detector movement systems can employ non-slipping translational drives that allow more precise positioning and greater speed.
Flatbed systems also have disadvantages related to their configuration. The support platen must be large enough to hold the largest document processable by the system. When smaller documents are placed on the transparent platen (most systems rarely image the largest possible document), large expanses of the transparent platen remain uncovered. This necessitates the usage of a platen cover, both to shield the user from bright imaging lighting and to avoid the creation of dark areas in the image when the original fails to cover the entire imaging area. The platen and platen cover are largely responsible for the relatively sizeable footprint of some flatbed systems.
The platen cover itself is bothersome. It must be hinged to swing open and closed, such that the hinges interfere when a user tries to offset an original towards the hinges. It must be opened and closed to insert each original. The act of closing it must be performed slowly to avoid displacing an original, and once it is closed, the original is no longer visible. The platen cover does not conform well to books and other thick originals. If the platen cover is not kept clean, it creates smudged areas in an image when it is visible in the imaging area.
Some of the problems of a platen cover can be avoided when a document feeder that automatically positions documents on the platen is incorporated into the cover. But the feeder increases the bulk of the platen cover that must be opened and closed, and the feeder belt visible through the platen makes it even more difficult to present a white background to the imager.
A flatbed document imaging system is disclosed that does not depend on a platen cover to reflect imaging light back into the system. The system uses a platen having an array of polymer/liquid crystal (PLC) segments. Each segment can be set to either a transparent mode or an opaque mode. When a segment is in the transparent mode, the imaging system can image through that segment of the platen. When a segment is in the opaque mode, imaging light impinging on that segment is diffused and largely reflected back into the system. Likewise, outside light is diffused and largely prevented from entering the system through an opaque segment. The system further comprises a segment controller and an imaging area calculator. The imaging area calculator instructs the segment controller as to the size and location of a desired transparent imaging area, and the segment controller sets the segments in the array accordingly.
In a second aspect of the invention, a document imaging system platen is disclosed. The platen comprises two transparent insulating plates, with each plate having a transparent electrode pattern formed on it. The plates are stacked with a gap between them, and the gap is filled with a polymer/liquid crystal filler. Regions of the polymer/liquid crystal filler lying between overlapping regions of a transparent electrode from each of the two plates form PLC segments.
In a third aspect of the invention, a method of operating a document imaging system is disclosed. The method comprises activating a subset of an array of PLC segments on a platen, thereby forming a transparent region and an opaque region on the platen. The transparent region can be selected to match the imaging region corresponding to a currently selected image size and magnification for the imaging system. The transparent region can alternately be selected to match the size and positioning of an original document placed on the platen. A user can also be provided controls for manually adjusting the transparent portion of the platen. The method may further comprise directing imaging light at the platen without covering the platen.